Method and apparatus for extrusion of thermoplastic handrail

ABSTRACT

A method and apparatus for extrusion of an article is provided. A die assembly can apply flows of thermoplastic material to an array of reinforcing cables to form a composite extrusion. A slider fabric can be bonded to one side of the composite extrusion. After exiting the die assembly, the slider fabric can act to support the extrudate as it passes along an elongate mandrel, which can cause the base of the slider fabric to change shape from a flat profile to the final internal profile of the article. The extruded article can then be cooled to solidify the material. The die can include cooling for the slider fabric and means for promoting penetration of the thermoplastic into reinforcing cables.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 14/744,690filed Jun. 19, 2015, now U.S. Pat. No. 9,981,415, which is acontinuation-in-part of U.S. application Ser. No. 13/593,859 filed Aug.24, 2012, now U.S. Pat. No. 9,579,839, which is a divisional of U.S.application Ser. No. 12/677,458, now abandoned, which is a NationalStage Entry of International Application No. PCT/CA2008/001596 filedSep. 10, 2008, which claims the benefit of U.S. Provisional ApplicationNo. 60/971,152 filed Sep. 10, 2007. U.S. application Ser. No. 15/578,741is a National Stage Entry of International

Application No. PCT/CA2016/050508 filed Jun. 17, 2016, which claimspriority to U.S. application Ser. No. 14/744,690. The entire contents ofeach are hereby incorporated herein by reference.

FIELD

This specification relates generally to thermoplastic handrails forescalators, moving walkways and other transportation apparatus, and to amethod and apparatus for manufacture of such a handrail or other articlethat has a substantially constant cross section by a continuousextrusion technique.

BACKGROUND

The following paragraphs are not an admission that anything discussed inthem is prior art or part of the knowledge of persons skilled in theart.

Handrails are a known and standard part of any escalator, moving ramp,moving walk or other similar transportation apparatus. Conventionally,such handrails are formed largely of rubber, which makes up the outercover of the handrail and forms a comfortable exterior “C” shape to begrasped by a user, and also include steel reinforcing cables and fabricplies, which act to provide dimensional stability to the handrail.

To locate the handrail and enable it to travel freely, it is providedwith a T-shaped slot on the underside. This slot engages a correspondingT-shaped section or guide made from polished steel, plastic or the likeand provided along the escalator, and at either end is engaged by largepulley wheels, curved guides, or rollers. Underneath the escalator,appropriate drive mechanisms are provided. To enable the handrail toslide freely, the T-shaped slot is conventionally lined with a fabric,which may be cotton or a synthetic material, which is usually referredto as a “slider”.

Additionally, handrails are usually reinforced longitudinally with steelcables or other relatively inextensible material, as a stretch inhibitorto provide sufficient resistance to stretching in the longitudinaldirection. A handrail requires the incorporation within the body of thehandrail of a number of reinforcing elements, or plies, to make thehandrail sufficiently stiff, at least laterally, to resist bothaccidental and deliberate derailment of the handrail from the guide,while not detracting from its longitudinal flexibility. These plies areusually fabric having orthotropic properties, that is, they exhibit acertain degree of stiffness in one direction while remaining moreflexible in the other. The stretch inhibitor at least must be reasonablyprecisely located and, more importantly, should generally be located ata uniform depth on a common neutral bending axis, so as to enable thehandrail to flex freely as it passes around pulleys etc. The handrailrequires the formation of a T-shaped slot, which additionally has to beprovided with a slider layer, which is bonded on just one side to thehandrail. The T-shaped slot must be accurately formed, to ensure thatthe handrail is securely retained in position in use.

Because of these requirements, handrails have traditionally beenmanufactured in a piece wise manner. This has also required the use ofrubberized fabric. The plies of rubberized fabric, cords and raw rubberare stacked together, assembled in a mold and compression molded underheat and pressure to cure and mold the composite into the characteristichandrail C-shape. The mold is typically of the order of 10 to 20 feetlong, enabling such lengths of handrail to be molded at once. Once eachsection has been molded, the handrail is moved forward by the length ofthe mold. The next section is then molded. In this manner the entirelength of a single handrail is fabricated and cured except forapproximately 5 feet at each end; these ends are then spliced together,molded and cured to form an endless handrail. This manufacturing processis laborious, requires considerable manual labour, and leads to aproduction rate dictated by the speed of curing reaction of the rubber,typically of the order of 10 minutes, and the length of the mold.

A handrail in use is located on a T-section member. The ability of ahandrail to withstand accidental or deliberate displacement depends to asignificant extent on the lateral stiffness or lip-strength of thehandrail. A major component of an extruded handrail is the elastomericmaterial, and a key factor is the hardness of the elastomeric material.Selection of the hardness of the elastomeric material, as well as othermaterials, is a compromise between lateral stiffness and longitudinalflexibility. The handrail must have sufficient longitudinal flexibilityto enable it to follow a handrail guide around turnarounds at the endsof an escalator or moving walk. It must also be capable of following thevarious pulleys through the drive mechanism and back underneath thehandrail.

Despite these requirements, as a handrail has a uniform cross-section,it theoretically could be made in continuous lengths, for later cuttingto size for individual applications; thus it can be suited to productionby an extrusion technique.

U.S. Pat. No. 4,087,223 to Angioletti et al. discloses an extrusiondevice and the continuous manufacture of a handrail of elastomericmaterial, C-shaped in cross section. The extrusion device is providedwith separate and distinct openings for the introduction of the variouselements of the handrail, and with means which shape continuously saidelements and arrange them continuously in mutual correct position intoelastomeric material.

U.S. Pat. No. 6,237,740 to Weatherall et al. discloses a moving handrailconstruction, for escalators, moving walkways and other transportationapparatus having a generally C-shaped cross-section and defining aninternal generally T-shaped slot. The handrail is formed by extrusionand comprises a first layer of thermoplastic material extending aroundthe T-shaped slot. A second layer of thermoplastic material extendsaround the outside of the first layer and defines the exterior profileof the handrail. A slider layer lines the T-shaped slot and is bonded tothe first layer. A stretch inhibitor extends within the first layer. Thefirst layer is formed from a harder thermoplastic than the second layer,and this has been found to give improved properties to the lip andimproved drive characteristics on linear drives.

INTRODUCTION

The following paragraphs are intended to introduce the reader to themore detailed description that follows and not to define or limit theclaimed subject matter.

A method of extruding an article of constant cross-section comprising afirst thermoplastic material, a stretch inhibitor and a web of fabric onone side of the article is provided. The method comprises the steps of:supplying the stretch inhibitor to a die assembly; supplying the firstthermoplastic material to the die assembly in a molten state, anextrusion temperature of the first thermoplastic material being below amelting point of the stretch inhibitor; bringing the first thermoplasticmaterial together with the stretch inhibitor, thereby to embed thestretch inhibitor within the first thermoplastic material; supplying anelongate flexible web fabric of constant width, the extrusiontemperature of the first thermoplastic material being below a meltingpoint of the fabric; bringing the fabric up against the firstthermoplastic material below the first thermoplastic material to supportthe first thermoplastic material, the stretch inhibitor and the fabricthereby forming a composite extrudate; and permitting the compositeextrudate to cool and solidify.

Another method of extruding an article of constant cross-section andcomprising a thermoplastic material and a web of fabric on one side ofthe article is provided. The method comprises: supplying thethermoplastic material to a die assembly in a molten state; supplying anelongate flexible web of fabric of constant width; extruding thethermoplastic material out of the die assembly to form an intermediateextrudate of intermediate cross-section, while maintaining thethermoplastic material at a temperature above the crossover temperatureof the materials such that the material is molten but sufficientlyviscous to be stable; and bringing the fabric up against thethermoplastic material and below the thermoplastic material to supportthe thermoplastic material, to complete the article of constantcross-section.

A method of forming a handrail by continuous extrusion comprises thesteps of: combining together a thermoplastic elastomer in a moltenstate, a stretch inhibitor and a reinforcing slider fabric, to form ahandrail of a desired cross-section, the thermoplastic elastomer beingabove a crossover temperature of the thermoplastic elastomer, so as tobe in an initially molten state but sufficiently viscous to be stable;and cooling the handrail along the length thereof from the exterior tosolidify a substantial external layer around the exterior of thehandrail and subsequently cooling and solidifying the interior of thehandrail to prestress the handrail thereby to provide improved lipstrength.

An apparatus for extruding an article of uniform cross-sectioncomprises: a die assembly having a first inlet for a thermoplasticmaterial, an entrance slot for introducing an elongate fabric forbonding to one side of the thermoplastic material, an outlet die forforming an extrudate comprising at least the thermoplastic material withan intermediate cross-section, and a primary mandrel extending from theoutlet die and having a support surface for supporting the extrudatewhile still in a molten state, with the fabric abutting the mandrel forrelative sliding movement, the support surface at one end adjacent theoutlet die corresponding to the profile of one side of the intermediateextrudate and progressively changing along the length of the primarymandrel to the final profile, at the other end thereof, the finalprofile corresponding to a desired final cross-section for theextrudate.

Another apparatus for extruding an article of uniform cross-sectioncomprises: a die assembly having an entrance for introducing a stretchinhibitor, a first inlet for a thermoplastic material, an entrance slotfor introducing an elongate fabric for bonding to one side of thethermoplastic material, a combining zone comprising a duct for combinedextrusion flow with the entrance opening into the combining zone andfirst and second primary manifolds connected between the first inlet ofthe die assembly and the duct, for supplying the thermoplastic materialinto the duct as a first flow from the first primary manifold on oneside of the stretch inhibitor and as a second flow from the secondprimary manifold on the other side of the stretch inhibitor, forembedding the stretch inhibitor within the combined extrusion flow, thefabric being brought up against the combined extrusion flow afterembedding the stretch inhibitor therein, and an outlet die forming anextrudate comprising at least the thermoplastic material and the stretchinhibitor.

A method of extruding an article of uniform cross-section and comprisinga thermoplastic material and at least one cable for inhibiting stretchof the article is provided. The method comprises: supplying the at leastone cable to a respective at least one tube, the tube comprisingupstream and downstream ends, and having a length extending between theupstream and downstream ends and an inner diameter; conveying the cablethrough the tube between the upstream and downstream ends; supplying thethermoplastic material to the downstream end of the tube; bringing thethermoplastic material together with the cable to embed the cable withinthe thermoplastic material, thereby forming a composite extrudate; andpermitting the composite extrudate to cool and solidify. At least one ofthe length and the inner diameter of the tube may be selected to atleast hinder movement of loose windings of the cable from the downstreamend towards the upstream end of the tube.

An apparatus for extruding an article of uniform cross-section andcomprising a thermoplastic material and at least one cable forinhibiting stretch of the article is provided. The apparatus comprises:at least one tube for respectively conveying the at least one cable, thetube comprising upstream and downstream ends, and having a lengthextending between the upstream and downstream ends and an innerdiameter; an inlet for the thermoplastic material; and a combining zonein communication with the downstream end of the tube and the inlet,wherein the cable is conveyed through the tube between the upstream anddownstream ends, and wherein the at least one cable is embedded in thethermoplastic elastomer in the combining zone. At least one of thelength and the inner diameter of the tube may be selected to at leasthinder movement of loose windings of the cable from the downstream endtowards the upstream end of the tube.

These and other aspects of this specification are applicable tohandrails, conveyor belts and a variety of other articles. For example,extrusion methods and apparatuses describe herein could be applied tothe production of door and other trim for vehicles, which can comprise athermoplastic material, a flocked surface, and optionally, a metalliclayer or the like. The cooling technique described herein has theadvantage of prestressing the extruded article. For handrails thisprovides improved lip strength. For door trim and the like, it can biasthe sides inwards, to provide better grip.

These and other aspects or features of the applicant's teachings are setforth herein.

DRAWINGS

The skilled person in the art will understand that the drawings,described below, are for illustration purposes only. The drawings arenot intended to limit the scope of the applicant's teachings in any way.In the drawings:

FIG. 1 is a perspective view of an extrusion apparatus;

FIG. 2a is a perspective view of a cooling tank and take up assemblyfora handrail;

FIG. 2b is a vertical sectional view of one end of the cooling tankshowing a water curtain;

FIG. 3 is a perspective view of a tube assembly for reinforcing cables,with other elements of the die assembly shown in ghost outline;

FIG. 4 is a schematic, perspective view showing formation of the profilewithin the die;

FIGS. 5 and 6 show progressive formation of the handrail profile afterexit from the die;

FIG. 7 shows a cross-section through the extrusion at the die exit;

FIGS. 8a to 8e show cross-sections through different finished handrailprofiles;

FIG. 9 shows a view looking back towards the die exit;

FIG. 10 is a perspective view showing part of a forming mandrel forforming the internal profile of the handrail;

FIG. 11 is a side view showing, in ghost outline, various passagewayswithin the die;

FIG. 12 is a plan view showing, in ghost outline, passageways within thedie;

FIG. 13 is a perspective of an element of the die assembly;

FIG. 14 is a side view of part of a cable supply unit, showingapplication of an adhesive, drying and preheating;

FIG. 15a is a perspective view from above and the rear of a dieassembly;

FIG. 15b is a perspective view from above and the front of the dieassembly;

FIG. 15c is a perspective view from below of the die assembly;

FIGS. 16a to 16f are perspective views showing progressive assembly ofdifferent components of the die assembly;

FIGS. 17a and 17b are perspective views from different ends of a cablemandrel forming part of the die assembly;

FIG. 17c is an end view of the cable mandrel of FIGS. 17a and 17 b;

FIGS. 17d and 17e are cross-sectional views along lines BB and AA,respectively, of FIG. 17 c;

FIG. 18a is a perspective view of a comb unit from one end, and FIG. 18bis a perspective view of the comb unit from another end;

FIG. 18c is an end view of the comb unit;

FIG. 18d is a cross-sectional view along lines DD of FIG. 18 c;

FIGS. 19a, 19b and 19c are perspective views of outlet die blocks;

FIGS. 20a and 20b are perspective views of an extrudate support block;

FIGS. 21a and 21b are perspective views of top die blocks;

FIG. 21c is a view from underneath of the top die blocks of FIGS. 21aand 21 b;

FIG. 22a is a perspective view of another cable mandrel;

FIG. 22b is an end view of the cable mandrel of FIG. 22a ; and

FIG. 22c is a cross-sectional view along lines AA of FIG. 22 b.

DESCRIPTION OF VARIOUS EMBODIMENTS

Various apparatuses or methods will be described below to provide anexample of an embodiment of each claimed invention. No embodimentdescribed below limits any claimed invention and any claimed inventionmay cover apparatuses and methods that differ from those describedbelow. The claimed inventions are not limited to apparatuses and methodshaving all of the features of any one apparatus or method describedbelow or to features common to multiple or all of the apparatuses ormethods described below. It is possible that an apparatus or methoddescribed below is not an embodiment of any claimed invention. Anyinvention disclosed in an apparatus or method described below that isnot claimed in this document may be the subject matter of anotherprotective instrument, for example, a continuing patent application, andthe applicant(s), inventor(s) and/or owner(s) do not intend to abandon,disclaim or dedicate to the public any such invention by its disclosurein this document.

Referring first to FIG. 1, an example apparatus is generally denoted bythe reference 20. The apparatus 20 includes a number of principalcomponents, including a die assembly 22, a cable supply unit 100, and amechanism 60 for mounting a roll of slider fabric.

For a handrail, the thermoplastic is a thermoplastic elastomer, of aselected hardness. As shown, the die assembly 22 has a main, primaryinlet 34 and a secondary inlet 70, for hot, molten thermoplastic. Theinlets 34, 70 can be outlets from conventional screw extrusion machines.Any suitable machines can be provided which are capable of providing thedesired material at the required temperature and pressure conditions. Asdetailed below, the machines must be capable of supplying the materialat desired flow rates.

Extending from the die assembly 22 is a mandrel 112, 134. As detailedbelow, the mandrel 112, 134 can be in a number of separate sections,which are connected together, and as discussed below, at least theleading portions are provided with a vacuum feed to ensure that thehandrail adopts a proper internal profile.

Referring to FIG. 2a , the mandrel 112, 134 passes into a trough or tank132 for cooling the handrail. On leaving the tank 132, the handrailpasses through a drive unit 150, and is then taken up on a take uproller 155.

Details of the die assembly 22 will now be described in relation toFIGS. 3, 4, 7, 9, 11 and 12. Firstly, as best shown in FIGS. 11 and 12,the die assembly 22 comprises a number of separate zones that areconnected together to form a complete die assembly.

In an inlet zone 24 the polymer from the inlet 34 is divided into twostreams or flows, above and below a cable array. Next to this, there isa choke zone 26 in which relatively narrow passageways are provided, tochoke the polymer flow and provide uniform back pressure, so that thetwo streams have substantially equal flow.

Next there is a cable combining zone 28. This comprises an upstream zone28 a in which the upper and lower streams of polymer are broughttogether above and below the cable array, and a downstream zone 28 b, inwhich the polymer uniformly sandwiches the cable array to embed thecables therein. As described below, a comb can be implemented togenerate back pressure to encourage the polymer to penetrate the cablearray.

The next zone is a slider combining zone 30. Here a layer of sliderfabric is brought up against the extrusion profile formed.

Finally, there is an outlet zone 32, in which a secondary flow ofpolymer is introduced and combined with the combined extrusion flow, forforming an outer layer of the handrail.

Referring now to FIG. 3, the first inlet 34 is connected to the outletof a conventional screw extruder; any suitable extrusion machine can beused which is capable of delivering the selected elastomer or otherthermoplastic at the required temperature and pressure conditions.Optionally, a melt pump could be used in addition to the screw extruder.Alternatively, a twin screw extruder could be used in place of theconventional screw extruder, the twin screw extruder enabling use of apolymer blend.

A short inlet duct 36 branches and is connected to bottom and topdistribution ducts 38, 39. FIG. 11 shows clearly the separate ducts 38,39 while FIG. 12 shows, in plan view how the ducts 38, 39 curve through90° and are connected to a first or bottom manifold 40 and a second ortop manifold 41. As such the inlet 34 provides a first inlet means. Itwill be appreciated that this first inlet means could alternatively beprovided by two separate extruders separately connected to the two ducts38, 39.

The manifolds 40, 41 distribute the flow evenly across the desiredwidth, and continue into a first or bottom and second or top chokes 42,43. The chokes 42, 43 can have a constant width, but, as seen in FIG.11, their depth can be considerably reduced, as compared to themanifolds 40, 41. The reason for this is to provide controlled flowresistance in each of the top and bottom channels, so as to ensuredesired flows through the top and bottom channels. The top choke 43 canhave a greater width than the bottom choke 42, so as to provide agreater flow. This effectively maintains the cable array towards thebottom of the combined extrusion flow, as desired.

The chokes 42, 43 continue into bottom and top combining ducts 44, 45.These ducts 44, 45 have a greater depth as seen in FIG. 11, and theirwidth tapers inwardly, as shown in FIG. 12, to a width corresponding tothe width of a slider fabric.

Now, as best seen in FIG. 3, an intermediate wedge-shaped block 46separates the chokes 42, 43 and combining ducts 44, 45. A plurality oftubes 48 are mounted in the block 46. The tubes 48 are dimensioned toclosely fit cables 50 for reinforcing the handrail, as detailed below,while permitting free sliding movement of the cables 50, as indicated byarrow 52 in FIG. 3.

The tubes 48 end at the downstream combining zone 28 b. Although notshown, adjacent the end of the tubes 48, there can be a comb extendingacross the duct. For test purposes with a relatively low productionrate, this comb can be provided to generate sufficient back pressure tocause the polymer to penetrate the cables 50. At higher productionrates, there will necessarily be higher pressures in the die and it isanticipated that these will be sufficient to generate the requiredinternal pressure to ensure good penetration of the polymer, so that thecomb can be omitted, as shown.

Downstream, in the combining zone 28 b there is a single rectangularsection duct 56. Thus, as shown in FIG. 11, the cables 50 as they leavethe tubes 48 are sandwiched between top and bottom flows of polymer, andcontinue to travel together down the duct 56.

It is to be appreciated that this arrangement with the polymer broughtup against the cables from two sides can be advantageous. It ensuresthat the cables will be positioned accurately and consistently in thefinished product and that they will not be displaced by any cross flowof the polymer. This arrangement also enables other forms of stretchinhibitor to be used. For example, a steel tape or tape comprising steelcables embedded in a polymer could be used. Where any tape (and a carbonfiber tape 174 is shown in FIG. 8b ) is used, it is important that thepolymer is supplied from both sides, to ensure accurate formation of thehandrail.

It is also possible for the steel cables to be formed into a compositetape, having a sandwich construction, in which the steel cables areembedded between two layers of polymer, and on either side there are twolayers of fabric to complete the sandwich. Such composite tape can beformed using an apparatus similar to apparatus described herein. Thus,steel cables can be fed into a die and polymer can be supplied above andbelow the cables. Separately, and after embedding of the cables in acomposite polymer flow, two tapes of the required fabric are broughtinto the die through slots, as for the slider fabric 62. Moreover, sucharrangement could be incorporated as an additional stage of the dieassembly 22. In effect, the composite tape would be formed continuously,upstream of the cable combining zone 28, and fed into that zone. Anadvantage of this technique is that it would enable a different grade ofpolyurethane or other polymer to be present in the composite sandwichand immediately around the cables. Such a construction is shown in FIG.8c , where the additional tapes or fabric layers are identified at 190and the additional polymer layer at 188.

A known problem in handrail construction is fretting of the cables. Incertain handrail drives, such as linear drives, the portion of the bodyof the handrail bearing the cables is subject to extreme pinching loadsas it passes through pairs of drive rollers. This can cause fretting ofcables and separation of the cables from the surrounding polymer. Othertypes of drives impart different loads. By separately embedding thecables in a composite tape and by selecting a polymer of a suitablegrade, one can tailor the characteristics of the handrail. It has beenobserved that use of a high pressure comb in combination with a semiflexible adhesive works well to penetrate the wires in each cable, andprotect each cable to prevent or at least reduce fretting.

With reference to FIGS. 1 and 11, a reel 60 for slider fabric is mountedon a shaft (not shown). The shaft would be connected to a drivemechanism for maintaining a desired tension in the slider fabric. Theslider fabric 62 leaves the reel 60 as a flat band. This slider fabric62 enters the upstream combining zone 28 a by an entrance slot 64. Theslot 64 has a corner 64 a which turns the fabric band throughapproximately 70°, and a further corner 64 b, after which the sliderband extends horizontally. The corner 64 a, 64 b can be coated withTEFLON™ or otherwise configured to reduce friction. Excessive frictiontends to stretch the slider fabric, resulting in pretensioning of it.This can make it difficult for a resulting handrail to bend backwards,when passing through a drive mechanism. After the corner 64, the sliderfabric 62 is brought up against the bottom of the composite extrudate 58and combined with it.

The slider fabric 62 is typically an elongate flexible web of sheetmaterial having a generally constant width. A relatively low coefficientof friction of the slider fabric 62 enables the handrail to slide overguides. The width of the slider fabric 62 depends on the size of thehandrail, and can be 125 to 60 mm wide, for example. In some examples,the slider fabric 62 can consist of woven material, either a naturalmaterial like cotton or a synthetic material such as polyester or nylon.However, it should be appreciated that the term “fabric” as used hereincontemplates other non-woven sheet materials that have suitableproperties.

It has been determined that the bending modulus of an extrudate productbased on a combination of thermoplastic elastomers and woven fabric canbe strongly dependent on the properties of the fabric. This isparticularly the case in a handrail where the neutral bending axis isdefined by a high modulus member (e.g., a cable array) of significantdistance from the fabric. The fabric can be subjected to a longitudinalpulling force in a crosshead extrusion process, which can cause thefabric to distort and stretch. This stretch is a function of the fabricproperties, applied force and temperature. In a crosshead extrusion die,the temperature of the die and molten polymer can be of a level thatwill weaken a synthetic woven fabric, and this can result in significantstretch even at relatively low loads. Once the fabric is stretched andcooled the properties are changed and locked in to the new product,which can have adverse effects on the properties of the product. Thefabric that has experienced significant process stretch will generallyhave a higher modulus and lower elongation to break than the fabricprior to processing.

The slider fabric 62 can be preshrunk. If it is not preshrunk, it hasbeen found that it can give limited performance in tension, especiallywhere the handrail is to be bent backwards in a drive mechanism;preshrunk fabric generally enables greater stretching of the fabric intension. Preshrinking can be provided by passing the fabric 62 betweenheated plates, immediately before it enters the die assembly 22.Furthermore, it has been found that preheating promotes adhesion of thefabric to the thermoplastic material.

An example of a method and apparatus for slider layer pretreatment isdisclosed in U.S. Provisional Patent Application No. 60/971,156, filed10 Sep. 2007 and entitled “Method And Apparatus For Pretreatment Of ASlider Layer For Extruded Composite Handrails”, and the correspondingInternational Application No. PCT/CA2008/001600 filed 10 Sep. 2008, theentire contents of both are incorporated herein by reference.

As shown in FIG. 4, the composite extrudate 58 initially extends acrossthe full width of the slider 62. In the combining zone 30 (FIG. 11), theedges of the slider 62 are folded upwards, so as to extend up the sidesof the extrudate, which is shown as a rectangular cross-section. Theeffect of this is to reduce the width of the extruded section orcombined extrusion flow 58 (FIG. 4), and its depth increasescorrespondingly, so as to maintain a constant cross-section.

FIG. 13 shows die inserts 160, which are mirror images of one another,and a part of the slider combining zone 28. The die inserts 160 serve toturn up edges 63 (shown in FIG. 5) of the slider fabric. Each die insert160 has a ramp surface 162, which is shown as flat or horizontal at oneend and progressively rotates through to a vertical position at theother end of the insert, to effect the turning up of the edge.

As indicated schematically in FIG. 11 at 164, it is also possible toinsert a breaker ply or additional ply into the handrail section. Ineffect, an additional ply of fabric is introduced between compositeextrudate 58 and a secondary flow from the inlet 70. Thus, as indicatedin FIG. 11, a slot similar to the slot 64 can be provided between theslider combining zone and the outlet zone. It will be furtherappreciated that this basic technique of providing two flows of thepolymer or polyurethane separately on either side of the fabric can beapplied in various ways. For example, an additional ply need notnecessarily be applied between the two flows from the first and secondinlets. It is possible, for example, for part of the flow from eitherone of those inlets to be branched off, to effect a sandwiching of anadditional ply between that branched flow and the main flow.

The secondary inlet 70, as for the other inlet can be connected to aconventional screw extruder, and again any suitable extrusion machinecan be used, optionally in combination with a melt pump. The inlet 70continues through a duct 72 into the outlet zone or block 32. The duct72 is connected to a standard manifold 74, known as a coat-hanger shapedmanifold, which distributes the flow substantially uniformly across thewidth of the composite extrudate or extrusion flow 58. The manifold 74,in section, shows two channels extending down either side of it and arelatively narrow section between the two channels, which sectionincreases in width from top to bottom.

FIG. 9 shows an end view of the die looking upstream. As shown, theoutlet zone 32 has a lower die member 80 and an upper die member 81secured together by bolts in bores 82, in known manner. The coat-hangershaped manifold 74 is indicated in dotted outline.

The lower die member 80 defines a rectangular channel 84 in which thefabric slider 62 is received with the composite extrudate. Toaccommodate the additional material from the second inlet 70 and to formthe required handrail profile, the upper die member 81 can define adouble-peaked curved profile 86.

The profile of the duct for the composite extrudate 58 (FIG. 4) upstreamof the manifold 74 is indicated by the line 88 (FIGS. 7 and 9). Theshape of this line 88 will depend upon the form of the handrail beingextruded. In this example, the inlet 70 and the extrusion machineassociated with it had a relatively small capacity, and hence thecross-section that could be filled from the inlet 70, i.e. the crosssection between the line 88 and profile 86, was restricted.

For smaller handrail sizes, the line 88 would be a straight line, sothat the composite extrudate 58, upstream in the manifold 74, would be asimple rectangle, as indicated in FIG. 7. As shown in FIG. 9, for largerhandrail sizes, the line 88 would include a trapezoidal centre section;in other words, the extrudate 58 would be caused to adopt the profile ofa rectangle with a super imposed trapezium. This occurs when the sidesof the slider fabric 62 are folded up. This has the effect of reducingthe effective cross-section to be filled from the inlet 70. As shown,the arrangement is such that the secondary material from the inlet 70always extends to the edge of the cross-section. It is intended thatonly the secondary flow be coloured as desired, as this forms theexterior of the handrail, and the primary flow can be clear oruncoloured. It will be appreciated that any combination of colouring andclear material can be used for the two flows. For example, where anadditional ply 164 is provided, the first flow could be coloured and thesecond flow clear, to enable a pattern on the additional ply to bevisible. The addition of the secondary flow is indicated schematicallyby the arrows 90 in FIG. 4.

The cable supply unit 100 is now described in relation to FIGS. 1 and14. There is provided a plurality of cable reels 102 each containing asingle, multi-strand steel cable, which can be of a type suitable forhandrails. The cable reels 100 can be mounted on shafts (not shown)including a means for braking, which maintain an appropriate tension inthe cables. Optionally, the cable reels 100 can be housed in atemperature and humidity controlled enclosure to prevent corrosion ofthe cables prior to adhesive application. The cables 50 can pass arounda turnaround roller 104 and then pass through an adhesive applicator106, although the turnaround roller 104 is optional.

It should be appreciated that handrails can generally shrink over time,which is due to the individual strands of the steel cables rubbing andwearing. The detritus, which can be primarily steel, fills theinterstices of the cable. Oxidation of the iron causes this material togrow which forces the cable to expand in cross-section and decrease inlength. Completely impregnating the cable with adhesive, with itsexcellent abrasion resistance, can prevent or at least reduce thiseffect.

The adhesive applicator 106 comprises a vessel 92 for holding a liquidadhesive solution. It has an inlet and an outlet 94, each of which hashard fibrous or sponge pads between which the cables 50 pass and whichare saturated with adhesive solution to promote penetration of theadhesive into the interior of the cables. The pads also serve to sealthe vessel 92. To provide a substantial adhesive coating, the applicator106 can include tubes, at the outlet side, through which the cables 50pass, the tubes being sized to provide the desired thickness ofadhesive. The adhesive applicator 106 can also serve to apply tension tothe cables. Before entering the die assembly 22, the cables pass overfans 96, which drive off the solvent, to leave the adhesive on thecables. The cables 50 then pass through a hot air tunnel 108 connectedto a fan with a heater 98 or other hot air source. This serves topreheat the coated cables 50 to a temperature of around 300° F., or suchother temperature as promotes good adhesion of adhesive. Infrared panelsor other heating devices could alternatively be provided. For clarity,the cables are shown spread apart as they pass around the roller 104;however, the cables can be substantially parallel and uniformly spacedas they pass through the adhesive applicator 106 over fans 96 andthrough tunnel 108.

Now, the section extruded out of the die assembly 22 is shown in FIG. 7and comprises an intermediate extrudate 110. The temperature conditionsin the die are such that, on leaving the die, the polymer is stillmolten, i.e. it is generally above a crossover temperature. Below thecrossover temperature, the shear modulus is greater than the lossmodulus of the material, while above the crossover temperature the lossmodulus is greater than the shear modulus. The shear modulus is theelastic-response component associated with the tendency of the materialto remember its predeformation dimensions, while the loss modulus is theenergy-dissipative response component and is associated with flow duringdeformation (see “Thermoforming Thermoplastic Polyurethanes”, byEckstein et al., Plastics Engineering, May 1995, page 29). Thetemperature is such that the polymer is still liquid but has a highviscosity. The polymer is thus largely stable in that it will maintainthe twin-peak rounded profile for some period of time, and will notrapidly slump to a flat profile. At the same time, it has thecharacteristic of a liquid, in that, as detailed below, it can be shapedand formed to alter the profile of the cross-section while not having atendency to return to its pre-formed shape. More particularly,relatively sharp angular features can be formed without difficulty.

There are at least two characteristics of a handrail that enables suchan extrusion technique to be adopted. Firstly, the handrail includes theslider 62. During passage along the mandrel 112, the slider 62effectively acts as a conveyor belt to support the still molten TPU. Atthis stage, the TPU is extremely sticky, so that if it comes intocontact with any solid surface, it tends to stick to it; in other words,it cannot be permitted to come in direct contact with the mandrel 112.Indeed, if any shaping roller or the like has to contact the TPU, thenthis must be cooled, so that the TPU, at least locally, is “skinned” toprevent sticking.

A second characteristic is that the handrail has a simple, roundedexternal shape. This shape can be readily formed on the mandrel. Incontrast, an external surface with a complex shape with protrudingportions, recesses and sharp corners could not be formed by such atechnique but rather would need to be formed by an appropriately shapeddie.

To shape the intermediate extrudate 110 into the final profile of thehandrail 126, an elongate primary mandrel 112 is provided. The mandrel112 comprises a number of sections. As FIG. 10 shows, the mandrel has abase 114 and an upper section 116 defining a support surface. Theprofile of the upper section 116 changes progressively and smoothly, toform the handrail profile. Extending longitudinally of the upper section116 is a bore 118 into which opens slots 120. A transverse port 122opens into the bore 118. The port 122 is connected to a vacuum source.This maintains a vacuum within the bore 118 in the range of 8 to 12inches of mercury. The purpose of the vacuum is to ensure that theslider fabric 62, and hence the extruded section, always closely followsthe mandrel 112. The level of the vacuum is determined by that necessaryto ensure good accurate following of the mandrel 112 profile, while atthe same time not being too high so as to create excessive drag. If ahigh degree of vacuum is used, then a higher tension has to be appliedto pull the handrail along the mandrel, and this can stretch the sliderfabric 62.

FIGS. 5 and 6 show progression of the profile. As shown in FIG. 5, theedges of the extruded profile are first dropped downwards, so as to havethe effect of lessening the twin peaks of the original profile in FIG.7. Note that the slider edges, indicated at 63 in FIG. 5 are up againstside portions of the mandrel 112. In FIG. 5, the modified intermediateextrudate profile is indicated at 110 a. These sides edges 63 arecontinuously supported along the mandrel 112. The sides of the profile110 a are progressively dropped down, to form part of the rounded endsof the C-shaped profile of the handrail, until they are vertical. Theythen continue to be turned inwards and upwards, to form the finalC-shaped profile of the handrail, as shown in FIG. 6. The exact lengthof the mandrel 112 will depend upon the intended production rate.

The mandrel 112 can be heated or cooled in order to maintain theextrudate at the ideal forming temperature. This can be done since thefabric web, which remains solid through-out the process, forms thecontact surface and the molten material is untouched and hence cannotstick to the material. Depending on the production speeds at which theextrudate travels across the mandrel 223, cooling may in fact benecessary to maintain the mandrel at an appropriate tool temperature,for example, 50° C.

At the end of the mandrel 112 the finished handrail profile 126 isformed, this handrail profile being shown in FIGS. 6 and 8 a. As noted,the material is maintained in a molten state along the mandrel. As isknown, thermoplastic elastomers and specifically thermoplasticpolyurethane do not have defined melting points. Rather, the materialhas a shear modulus, which is the elastic-response component associatedwith the tendency of the material to behave elastically and remember itspredeformation dimensions, and also a loss modulus which is theenergy-dissipative-response component and which is associated with flowduring deformation. The ratio between these two factors or moduli,sometimes expressed as tan δ (delta), is indicative of the state of thematerial. When tan δ is much less than 1, then the material behaves as asolid and when tan δ is greater than 1 the material behaves as a viscousfluid. These two moduli change progressively over a significanttemperature; for example a polyurethane with a molecular weight of152,000 shows a progressive decrease in the value of both moduli over arange from about 150° C. to over 200° C., with the shear modulusdecreasing more rapidly than the loss modulus. Consequently, at atemperature of around 165° C., the value tan δ exceeded 1, indicatingthat the viscous properties were then dominant. In general, the materialshould have tan δ exceeding 1 along the whole length of the mandrel. Forsome applications it may be acceptable to have the material slightlybelow this point for at least part of the length of the mandrel. Also,due to heat loss from the exterior, the temperature of the outside ofthe handrail will be less than the temperature on the inside and it isthe internal temperature around the T-shape slot that is critical asthat is where relatively complex changes in the profile occur. The outerlayers are merely subject to relatively gently curving. Hence, it isacceptable if the outside begins to “skin” slightly, i.e. it starts tosolidify. However, at the end of the mandrel 112, the polymer is stillnot properly solidified. The original twin-peaked profile of theintermediate extrudate, in FIG. 7 is selected so that at the other endof the mandrel 112, the desired final profile is obtained.

Accordingly, to cool and solidify the polymer, it is now passed into acooling unit 130 including a cooling trough 132 (FIG. 2a ). As indicatedin FIG. 1, the tank 132 includes a secondary mandrel 134. This secondarymandrel has a profile of the finished handrail 126. At least the firstpart of this mandrel is slotted and has a bore, as for the mandrel 112,and is also connected to the vacuum source. In this example, the coolingtank 132 is 12 feet long, and the mandrel 134 has a correspondinglength; the exact length will depend upon the production rate. The first3 feet of the mandrel 134 in the tank 132 are slotted and connected tothe vacuum source. The reason for this is to ensure that the handrailclosely follows the mandrel 134, until it has been cooled sufficientlyso as to be fully stable and at least partially solidified, so as toretain its shape.

As shown, the tank 134 is provided with a spray bar 136 having an inlet138 and a plurality of spray nozzles 140. In some examples, referring toFIGS. 2a and 2b , at the entrance to the tank 134 a slot-shaped nozzle142 can be provide a water knife or curtain. This can enable immediateand uniform skinning of the extrudate, in case the extrudate is notskinned at this point. If it is still not skinned and is subject to aspray, the individual droplets tend to mark the surface. By applying auniform curtain or knife of water, this problem is avoided and a skin ofgenerally solid material is formed. Once this skin is formed, thehandrail can be readily cooled with a random spray without affecting theexternal appearance. The nozzle 142 can direct a curtain of waterinwardly at a slight angle to the handrail, so as not to mark it. Asupply chamber 144 in a generally circular element has an inlet 146 forwater, for the curtain 146.

Instead of a water knife, a water source such as a single nozzle (notshown) can be used to wet with cooling water the first, upstream roller148. A plurality of rollers 148 can be implemented to cool and effectthe skinning of the exterior of the extrudate and the removal of dielines. The rollers 148 are driven by the extrudate. Water applied to theextrudate by the first, upstream roller 148 can collect on the extrudatesurface between the first upstream roller 148 and the second, downstreamroller 148. The second, downstream roller 148 can also be used to shapethe outside surface of the handrail.

In use, water is sprayed through the spray nozzles 140 to cool thehandrail 126. The tank 132 includes a drain for the water, which iseither discharged, or passed through a cooling unit for return back tothe inlet 138. Water from the spray nozzles 140 can cool the handrail126, so as to solidify the polymer. This has been found to improve thelip strength of the handrail 126. While the reasons for this are notfully understood, one possible explanation is given below.

As the handrail 126 is cooled, the outside will solidify at first, andas is known, during solidification, the material will shrink or becomemore dense. Thus, initially, there will be an outer layer that issolidified, and the interior will still be molten. Note that, in someexamples, the mandrel 134 itself need not be cooled. When the interiorof the handrail 126 cools and solidifies, it will in turn attempt toshrink or become more dense. This is believed to have the effect ofprestressing the handrail, so that the lips, indicated at 129, in FIGS.8a, 8b and 8c , are urged towards one another. It is further believedthat the handrail profile is maintained by the slider fabric 62. In anyevent, for a given hardness of material, it has been found that improvedlip strength can be obtained.

It also has been found that the amount of heat removed from theextrudate can be important, and the timing of the removal of this heat.It has been found that for effective prestressing, heat can be removedpredominantly from the outside of the handrail and that this heatremoval should take place before the remaining heat is removed from thehandrail. Sufficient heat can be removed, to solidify a substantiallayer around the outside of the handrail, so that subsequent cooling,and hence shrinking, of the interior effects prestressing. Provided thisamount of heat is removed from the exterior first, the outer layers ofthe handrail can be sufficiently cooled and solidified that, when theinner part of the handrail solidifies, the prestressing occurs. Here,the arrangement with the water spray will remove heat almost exclusivelyfrom the exterior; there may be some minor amount of heat removed fromthe interior, but this is purely incidental. In the example illustrated,no attempt is made to remove heat through the mandrel 134 (FIG. 2a ),but on the other hand, no steps are taken to specifically insulate themandrel 134 to prevent such heat loss. However, as mentioned above, thecooling may be necessary to maintain suitable tool temperatures whileoperating at full speed.

Commonly, it is required for handrails to have a lip strength, and inaccordance with standard tests, in excess of 10 kg, this being todisplace the lips apart by a prescribed amount. Here, it has been foundthat, if the handrail is allowed to cool naturally and evenly from boththe interior and the exterior, the lips can be too weak to meet thistest; on the other hand, with the prestressing effected by this coolingtechnique, a lip strength greater than 10 kg and in the range 10 to 20kg can be achieved, which is comparable to conventional handrails.

The lip opening force of the handrail extruded by the method andapparatus disclosed herein can be typically 15 kg, and can be at leastthan 10 kg for a 7 mm deflection when measured with 30 mm jaws, for athermoplastic polyurethane of a hardness 85 Shore ‘A’. This is comparedto approximately 6 kg for a homogeneous non-prestressed sample,fabricated by compression molding with even heating and cooling.

On leaving the tank 132, the handrail 126 passes through a drive unit150. The drive unit 150 includes upper and lower drive assemblies 151and 152, each of which includes a band mounted on rollers, which bandsengage the handrail 126. The lower drive assembly 152 can be configuredto engage the slider on the inside of the handrail. Such units areconventional for extrusion molding. Here, the drive unit has a DC motorwith tachometer feedback, so as to give accurate control on the speed ofthe handrail. In some examples, this can give speed control accurate towithin 0.1%.

As is known in the extrusion art, if the extrusion speed is controlledcarefully, and the flow rates through the two inlets 34, 70 are alsocontrolled carefully, then the profile of the extruded handrail 126 andits weight per unit ft can be constant within desired tolerances. Withgood control, a weight tolerance better than 1% per unit length can beachieved. The extrusion machines are operated with a constant screwspeed to provide the necessary constant flow rate, which will beachieved if other factors, e.g., temperature, pressure, etc., areconstant. Use of melt pumps can further improve control and surgereduction.

As indicated at 155, a spool is provided for taking up the finishedhandrail 126. To form a loop of handrail, a selected length of handrailcan be spliced, for example, as disclosed in the U.S. Pat. No.6,086,806, entitled “Method Of Splicing Thermoplastic Articles”, theentire contents of which are incorporated herein by reference.

FIG. 8a shows the final finished profile of the handrail 126, with thecables 50 and slider fabric 62. The thermoplastic elastomer is formed astwo layers, an inner layer 128 being the thermoplastic supplied throughthe first inlet 34 and an outer layer 127 being the thermoplasticsupplied through the second inlet 70. The cables 50 can be disposed inthe inner layer 128 in a coplanar arrangement, the cables 50 definingthe neutral bending axis for the construction 126.

Now, with regard to exemplary materials, the slider fabric 62 can beplain weave spun polyester with a weight of 20 ounces per square yard.

Cables can be selected to have a relatively open construction to allowthe adhesive to penetrate the wire. For example, suitable steel cablescan each comprise a core of three strands of 0.20+/−0.01 mm, and 6 outerstrands of 0.36+/−0.01 mm. High tensile steel cord, brass plated, withsuitable specifications can be obtained from Bekaert SA, of Kortrijk,Belgium.

The adhesive used can be a solvent-based adhesive, although any suitableadhesive, for example a reactive hot-melt adhesive could be used. Theadhesive applied to the cables can be, for example but not limited to,THIXON™ 405 supplied by Morton Automotive Adhesives, a division ofMorton International Inc.

As to the thermoplastic elastomer, both layers 127 and 128 can be ofLubrizol ESTANE™ 58206 having an 85 Shore ‘A’ hardness. For certainapplications, it may be desirable to form the outside of the handrailwith a harder thermoplastic, and for this purpose, Lubrizol ESTANE™58277 with a 45 Shore ‘D’ hardness can be used; the inner layer 126could then be a softer material, such as Lubrizol ESTANE™ 58661 with a72 Shore ‘A’ hardness. For external applications, where the handrail maybe exposed to rain and the like, a polyether type water-proofthermoplastic can be used for the outer layer 127, such as LubrizolESTANE™ 58300, which has a hardness of 85 Shore ‘A’. Lubrizol ESTANE™58226 may also be suitable for some applications. Other thermoplasticmaterials are possible.

FIGS. 8b and 8c show variants of the handrail section. In FIG. 8b ,second handrail section 170 includes the slider 62 and inner and outerlayers 171 and 172 of thermoplastic. Here, the individual cables 50 arereplaced by a carbon fiber tape 174.

In a third variant of the handrail indicated at 180 in FIG. 8c , theslider 62 is again present as before. The handrail 180 has an innerlayer 181 and an outer layer 182. Here, the stretch inhibitor isprovided by a matrix 184, which comprises cables 186 embedded in a layerof thermoplastic elastomer 188. On either side of the elastomer 188there are fabric plys 190, to form a sandwich construction. As discussedabove, this sandwich construction can be formed at an entrance part ofthe die assembly, as an integral part of the die assembly, as anintegral part of the whole handrail forming process.

Modified handrail profiles 126 a, 126 b are shown in FIGS. 8d and 8e .In comparison to handrail 126, handrails 126 a, 126 b may exhibit lesscable buckling under severe flexing conditions, reduced strain andbending stresses and increased fatigue failure life under cyclic loadingconditions, as described in the U.S. Provisional Patent Application No.60/971,163 filed 10 Sep. 2007 and entitled “Modified Handrail”, and thecorresponding International Application No. PCT/CA2008/001599 filed 10Sep. 2008, the entire contents of both are incorporated herein byreference.

The profile of the curve 86 can be chosen so that, after travel alongthe mandrel 112, the desired profile is obtained. It will be appreciatedthat this profile will not always be accurate. To allow for this, one ormore trimming or sizing rollers can be provided, as indicated at 147 and148 in FIG. 2d . Thus, at least one set of rollers 147 can be providedto ensure that the overall width is within certain tolerances. At leastone roller 148 can be provided to ensure that the top thickness iswithin a desired tolerance. Contacting the handrail with rollers isacceptable at this point, since it is cooled sufficiently to have anexternal skin, and the rollers will not tend to stick to the material ofthe handrail.

In some examples, the rollers can be essentially cylindrical. However,at least the top roller 148 can have a profile corresponding to adesired profile for the top of the handrail, i.e. it would define thecrowned top surface of the handrail. The variation in diameter of aroller should not be too extreme, as this will cause slipping betweenportions of the roller and the handrail.

To reduce friction, various components can be coated with TEFLON™, orotherwise treated, to give a low coefficient of friction. Thus, thecorners 64 a, 64 b (FIG. 11) can be coated with TEFLON™. Similarly, themandrel 112, and at least the first part of the secondary mandrel 134can be coated with TEFLON™. Due to the vacuum, there can be a strongpressure pressuring the slider fabric 62 against the mandrels, which cangenerate a significant frictional effect.

While the teachings herein have been described primarily in relation toa handrail for an escalator or the like, it is to be appreciated that itis applicable to a variety of elongate articles of constantcross-section. More particularly, it is applicable to such articles,which have a main body formed from a thermoplastic elastomer withreinforcing or stretch inhibiting means running through it, and withsome additional sheet layer of fabric or the like bonded to one side.Such a construction is often found in conveyor belts. Typically,conveyor belts will be generally of rectangular cross-section, withapproximately uniform properties across the width of the conveyor belt.

Accordingly, it is not usually necessary to form a conveyor belt intoany complex profile, as for a handrail. Hence, the forming process onthe mandrel 112 can be omitted. The method described herein then enablesa conveyor belt to be formed in which reinforcing cables or the like areaccurately positioned, on a common neutral bending axis, at a desirabledepth within the main body of the conveyor belt, and the belt can have afabric layer bonded on one side. Again, such a conveyor belt can bespliced, as in the co-pending application mentioned above.

The polymeric material used could be any appropriate thermoplasticelastomer. Experiments and testing have shown that a thermoplasticpolyurethane (TPU) of hardness 85 Shore ‘A’ is suitable for handrailmanufacture. When this material is used to form the bulk of thehandrail, its adhesion to the slider fabric is acceptable without theneed for adhesives or glues. If the slider material is woven spunpolyester fabric the adhesion to the TPU in the final product istypically 60 pounds per inch of width (p.i.w) on a 90° peel test. Forexample, a polyester fabric was extruded through the die with the dietemperature set at 200° C., adhesion was measured at 20 to 30 pounds perinch width, whereas with the die at 215° C., adhesion was measured at 55to 60 pounds per inch width.

For these tests, a lightweight polyester with a monofilament weft wasused. Generally, monofilament materials pose greater problems inproviding good adhesion. Bench tests were done, molding fabric onto TPUin a heated press. The TPU was predried at 110° C. At press temperaturesof 215° C., the TPU thoroughly impregnated the fabric, but despite thisthe peel strength was only 20 pounds per inch width. On the other hand,preheating of the fabric to 200° C. and the TPU to 215° C. andsubsequent lamination gave samples with adhesions of over 65 pounds perinch width.

Also note, as in FIG. 11, an additional ply of fabric 164 may be addedfor product design flexibility as it can be added in any location in thethickness of the handrail where the flow in the die is split, such as isdone with the reinforcement.

It should be appreciated that this specification can provide anextrusion technique that enables the colour of a handrail, or otherarticle, to be quickly changed, either by changing the colour of thesecondary flow, or by changing an outer sheet layer, where this isprovided.

It should also be appreciated that this specification can provide anextrusion process that is separated into a number of steps each of whichis inherently simple, so that it is not necessary to attempt to effectnumerous complex extrusion operations simultaneously. The actualextruded profile can be relatively simple, and the technique is suchthat all elements can be accurately located in the correct position inthe extrusion profile. The slider fabric of a handrail can be used as aconveyor belt to support the extrudate during formation of the finalhandrail shape. The final form of the handrail shape can be formed byprogressive change of what becomes the interior handrail, and withoutnecessarily contacting the exterior profile, which enables the exteriorto cool and solidify to a high gloss finish. The exterior can be cooledby spraying with a fluid, for example water, so as to pre-stress thelips, to provide adequate lip strength. Furthermore, cooling of theextrusion die components related to the slider fabric can be cooledwhich limits the stretch of the fabric and enables a flexible handrailproduct.

The teachings of this specification can enable a handrail to be producedcontinuously and simply, without requiring the extensive manual settingup procedures required for conventional handrails. With polyurethaneused as the polymer, a grade can be selected that provides both adesirable, high gloss finish, and is resistant to cuts and abrasion, soas to maintain a high gloss finish.

The structure of the handrail can be simple unlike conventionalhandrails, and does not require elaborate combinations of plies to givethe required strength and durability characteristics. Rather, the use ofthe external cooling effects prestressing of the lips, so that even witha relatively soft grade of polyurethane, adequate lip strength can beobtained.

It has also been found that by combining the slider fabric and thepolyurethane together at elevated temperatures, excellent bondingcharacteristics can be achieved giving greater peel strength thanconventional bonding techniques.

The handrail can be produced in indefinite lengths. To form a completeloop of handrail, it can be spliced together, for example, as disclosedin U.S. Pat. No. 6,086,806. This splicing technique can provide a splicethat is not detectable by an ordinary user, and which can maintain thecontinuous, high gloss finish and appearance of the handrail.

The provision of two separate flows to the die assembly enablesdifferent polymers to be provided. It is only necessary for thesecondary flow, which forms the outer layer, to have the desiredappearance and colour characteristics. The main flow can comprise anysuitable material, and need not be colored. It could include recycledmaterial, which may come in a variety of different colors. For outdooruse, it is possible to provide the external layer with a weatherresistant polyurethane, while this is not required for the main flowthrough the first inlet.

A further aspect of this specification is the realization that, whenmanufacturing a handrail, the tolerances on the T-shaped slot with aslider can be much tighter than the tolerances on the external profile.Commonly, the T-shaped slot has tolerances of 0.5 mm, whereas there maybe tolerances of 1 mm on the external profile. It will be appreciatedthat the T-shaped slot has to follow correspondingly shaped guides, andhence tolerances can be critical. On the other hand, the exteriorprofile, at most, contacts drive wheels, where large tolerances canreadily be accommodated. Also, at the ends of the usable top run of ahandrail, the handrail will emerge from an aperture and then passthrough another aperture taking it under the escalator. These aperturesare dimensioned to prevent users fingers etc. from becoming trapped, butagain, tolerances on the external profile for this purpose arerelatively generous. Therefore utilizing hard-tooling for sizing theinternal surface can be sufficient.

Reference will now be made to FIGS. 15 to 18, which show details ofanother example of a die assembly being generally indicated by thereference 200. The die assembly 200 has an entry or entrance for astretch inhibitor or reinforcement, such as steel cables or steel tape,indicated at 202 and provided at the rear of the die assembly in cablemandrel 300, detailed below. At the front of the die assembly 200, thereis an outlet opening 204 for the extrudate. As with the first exampledescribed above, the steel cables 50 may be supplied from the cablesupply unit 100, which may be housed in a temperature and humiditycontrolled enclosure.

A first inlet 210 is provided for a primary polymer and a second inlet212 is provided for a secondary polymer. As detailed below, the dieassembly 200 comprises a number of separate elements that are securedtogether in known manner. These elements can be bolted together orotherwise secured to each other, with appropriate seals, to preventleakage of molten polymer. FIGS. 16a to 16f detail the individualcomponents of the die assembly 200, showing how they are built up toform the complete die assembly; additionally, the cable mandrel 300 isshown in detail in FIGS. 17a to 17e , and a comb unit 400 is shown inFIGS. 18a to 18 d.

Referring first to FIG. 16a , there is shown a first runner plate 220.The first runner plate 220 is formed with an first inlet runner 222that, in known manner, would be connected by the inlet 210 to a sourceof molten thermoplastic or polymer; as before, the thermoplastic orpolymer will, commonly, be supplied from a screw extruder or the like.As shown, the one first runner plate 220 is generally cylindrical, andhas cylindrical bore 224 for receiving the cable mandrel 300. As shownin FIG. 16a , the cable mandrel 300 has a cylindrical plug portion 302that matches the cylindrical bore 224, and also includes a circularflange 304 for bolting the cable mandrel 300 to the first runner plate220.

As shown in FIG. 16a , the first inlet runner 222 has a bore that opensinto a semicircular channel 226 on a front face 228 of the first runnerplate 220. As indicated by arrows, the channel 226 is intended to directflow of the molten polymer in the direction of the arrows.

Referring to FIG. 16b , another first runner plate 240 has a rear face(not shown) corresponding to the face 228 of the first runner plate 220and also provided with a semicircular channel to form a runner channel,which faces are mounted and sealed to one another. The other firstrunner plate 240 includes openings 242 that extend from that rear faceto a front face 244. The front face 244 is provided with recesses 246that form channels or manifolds directing the polymer flow towards thecentre of the face 244, and thus around the reinforcement or stretchinhibiting cables, again indicated at 50.

Turning to FIG. 16c , a comb plate 250 is mounted to the front face 244of the other first runner plate 240. The comb plate 250 has an elongatedrectangular slot 252, in which is mounted a comb unit 400. The slot 252will have a profile corresponding to that for the comb unit 400 asshown. The purpose of the comb unit 400 is to maintain the steel wiresor cables 50 in alignment and to provide slots of reduced flowcross-section to create a desired back pressure in the polymer flow, sothat the polymer is caused to penetrate the individual strands of thewires of cables 50.

The comb unit 400 is also configured to enable the production of acoplanar reinforcement array. This is achieved by controlling andlimiting cross flows, which tend to distort an array of cables. Moreparticularly, the comb unit 400 includes a diverging exit channel 402that prevents cross flows.

Between the other first runner plate 240 and the comb plate 250, thereis formed a first combining chamber or zone, in which the cables 50 arecombined with the first polymer flow, so as to be embedded therein.

Details of an inlet runner arrangement for a second polymer flow areshown in FIGS. 16d and 16e . A second inlet runner 260 provides a flowof a second polymer from the inlet 212 to a runner defined between apair of second runner plates 262 and 264. As shown in FIG. 16d , thesecond runner plate 262 has a recessed portion 266 on a front face 268defining a flow area or manifold that diverges to provide a uniform flowacross the width of the extrudate section comprising the primary polymerand the reinforcing wires or cables 50. The second inlet runner 260 iscompleted by the second runner plate 264, that is a plain plate. Thesecond inlet runner 260, as for the first polymer, would be connected toa suitable source of a secondary polymer, e.g., a screw extrusionmachine or the like.

The second inlet runner recess or manifold 266 opens into a secondcombining zone or chamber 270, that is also defined by a bottom element272. The bottom element 272 comprises first and second parts 274 and276; as one of these parts 274, 276 defines part of the chamber 270, twoparts 274, 276 are provided, to facilitate cleaning. As shown, thesecond part 276 is recessed at 278 as to form a slot into which a web ofthe slider fabric, indicated at 280, can be drawn. The first part 274may be, to at least some extent, thermally isolated from the second part276, to reduce heat transfer to the slider fabric. Increasing thetemperature of the polymer before contact with the relatively coolslider fabric may promote adhesion of these components in the extrudate.

Referring to FIGS. 16e and 16f , the extrudate then passes to an outletzone 282 that includes first and second bottom die blocks 284 and 286.These die blocks 284, 286 define a channel 288, into which is mounted anextrudate support block 290. This block 290 is provided with openings292 for coolant flow. The coolant may be water or oil. Additionally, theextrudate support block 290 can be mounted so as to be spaced from thebottom die blocks 284, 286 to reduce heat transfer to the extrudatesupport block 290 from the bottom blocks 284, 286. Ceramic coatings canalso be used.

In some examples, the cooling block 290 can be formed of steel. In otherexamples, the cooling block 290 can be formed of a high temperatureplastic, for example but not limited to, CELAZOLE™ or TORLON™. Hightemperature plastics typically have a relatively low heat capacity andheat transfer coefficient, resulting in less heat transferred to theslider fabric in the die. However, steel may be the preferred materialfor the cooling block 290 for its lower cost, each of fabrication andwear properties.

To assist in guiding the slider bearing the extrudate, the top surfaceof the extrudate support block 290 can be provided with two shallowrectangular slots or guides 294. As shown in FIG. 16e , side edges ofthe block 290 are slanted inwards, to progressively cause the side edgesof the slider fabric 280 to fold up, and roll around edges of the moltenthermoplastic.

FIG. 16d shows the location of the die where the secondary polymer flowand the fabric are added. The secondary polymer is spread over theprimary polymer and reinforcement in a manifold. The fabric 280 entersthe die from the bottom and is brought up under the combined polymersand reinforcement array. The fabric is supplied to the die at atemperature lower, and it may be significantly lower, than the melt ordie temperatures, approximately 50° C. This limits the maximumtemperature the fabric will achieve in the process. The fabric can alsobe supplied preshrunk and at, effectively, zero tension by providingfeed devices immediately outside the die. Further details of suitableslider pretreatment are provided with reference to U.S. ProvisionalPatent Application No. 60/971,156 filed 10 Sep. 2007 and entitled“Method And Apparatus For Pretreatment Of A Slider Layer For ExtrudedComposite Handrails”, and the corresponding International ApplicationNo. PCT/CA2008/001600 filed 10 Sep. 2008.

Referring to FIGS. 16d and 16f , to complete the outlet zone 282, a topdie block 296 is mounted above the first outlet die block 284, and apair of top die blocks 297 and 298 are mounted above the second bottomdie block 286.

The top die blocks 296, 297, 298 can be, to at least some extent,thermally isolated from the bottom die blocks 284, 286, e.g., by beingprovided with spacing, and these in turn are spaced or otherwisethermally isolated with respect to the extrudate support block 290. Thetop die blocks 296, 297, 298 can be heated by band heaters to keep theextruded thermoplastic polymer of a desired temperature. It will beunderstood that any thermal isolation will never be perfect and at bestwill only reduce heat transfer.

The cable mandrel 300 is shown in FIGS. 17a to 17e . As mentioned, itincludes a cylindrical plug 302 and a flange 304. Within the plug 302,there is an internal bore 306.

At the end of the cylindrical plug 302, a plurality of small bores 308are provided in a common plane. Each of these bores 308 has a portion ofsmall diameter and a portion of larger diameter. Thin walled hypodermicsteel tubes 310 are mounted in the smaller diameter sections of thebores 308. The steel tubes 310 can be replaced individually as required.

As shown, the front of the cylinder plug 302 shows a slightly protrudingridge section 312, with the ends of the tubes 310 opening onto the topof this ridge section 312.

To assemble the components of the die assembly 200, appropriate bores,threaded, plain or otherwise, can be provided for assembly purposes, inknown manner.

The comb unit 400 is shown in detail in FIGS. 18a to 18d . The comb unit400 essentially comprises first and second rectangular blocks 404 and406. The diverging exit channel 402 is provided on the top surface ofthe second rectangular block 406, with the top surfaces of the blocks404, 406 otherwise being coextensive.

In the middle and extending up to the top surface of the firstrectangular block 404, there is a comb section 410. This comb section410 is defined by rectangular slots 412 and 414. The slots 412 can beprovided towards the outer sections of the comb 410 and extend throughthe full depth of the comb section 410.

In the middle of the comb section 410, the slots 414 extend part waythrough the comb section 410, and below them, there are two horizontalslots or openings 416, as shown best in FIGS. 18c and 18d . In thisexample, there are 18 slots 414 and 10 slots 412, for a total of 28slots. There are twenty (20) steel cables or wires 50 in this example,and these pass through the top horizontal opening 416 to keep them inone plane.

The first polymer is delivered through the first runner plate 220 and isforced to pass through the slots 412, 414 and slot openings 416, nototherwise occupied by the steel cables 50. This can serve to generateback pressure, and force the polymer or thermoplastic into theinterstices between the individual strands of each wire, cable orstretch inhibitor 50.

It is to be noted that while this described example has 20 cables and 28slots 412, 414 are provided in total, these numbers could vary asdesired. Additionally, this arrangement can be modified to accommodateother types of stretch inhibitor. For example, for a steel tape stretchinhibitor, it would be necessary to have one single horizontal slot toaccommodate such a stretch inhibitor. For some applications, it mightprove preferable to first pass the steel cables through an extrusionmachine to form a molded thermoplastic strip in which the steel cablesare already imbedded. Such a thermoplastic strip would be of generallyrectangular of cross section and would be supplied to the suitableextrusion apparatus for extruding the complete handrail cross-section inmuch the same manner as a steel tape stretch inhibitor.

In use, the steel cables 50 can first be processed to provide them withadhesive, e.g., a modified epoxy adhesive, as shown in FIG. 14, or asimilar technique. The steel cables 50 are then supplied to the tubes310 of the cable mandrel 300. Simultaneously, a first polymer issupplied to the first runner plate 220 and is delivered through thechannels 226 to the combining chamber 234, where it flows around eitherside of cables 50 to in embed the cables 50 in the thermoplastic flow.

The combined steel cable and thermoplastic flow then passes through thecomb section 410 of the comb unit 400. The restricted flow cross-sectionof the comb section 410 can cause significant back pressure, that canserve to force or pressurize the thermoplastic into the spaces orinterstices in between the individual strands of the cables 50.

After passing through the comb unit 400, the first thermoplastic flowwith the steel cables 50 enters the second combining chamber or zone270, where the second polymer flow is supplied to form a top layer onthe extrudate, this second polymer flow being supplied from the secondinlet 212 and through the second inlet runner 260.

As the flow passes over the extrudate support block 290, it meets thefabric web 280 introduced through the slot 278 and these are combined inthe outlet zone 282.

The entire die assembly 200 can be uniformly heated with standard bandheaters and the temperature is controlled between 175° C. and 210° C.,for example. The two parts of the die 284, 286 below the cooled block290 need not be heated, and the contact of these to the upper final dieparts can be minimized. Heat can be applied to the final zone of the diefrom the top only. This enables the greatest possible temperaturedifference between the parts of the die that contact the molten polymerand the cooled block which contacts the fabric. Using the configurationas shown allows the cooled block 290 to be held at a temperature below75° C., with the rest of the die at 200° C. Contact with the moltenpolymer still causes a temperature increase but this is much less thanwithout the cold zone. Using this setup it is possible to control thefabric stretch in the die to less than 4%.

It will be understood that while exemplary temperatures and otherparameters have been given, these temperatures and other parameters canbe varied depending upon characteristics of materials used and otherparameters.

The completed extrudate exits the die through the final opening 204, andcan then pass to the support mandrel as shown in earlier figures.

Further processing of the extrudate to form the desired shape, e.g.,shaping into an extruded handrail on the mandrel, can then take place asdescribed above. The mandrel or former need not be secured to the die,and it is possible to provide for some relative displacement between thedie assembly and mandrel.

Referring to FIGS. 19a, 19b and 19c , the outlet die blocks 284 and 286can be integrally formed with one another. As shown, the die blocks 284,286 have a base portion 320 and side portions 321 and 322, which can bemirror images of one another. Each side portion 321, 322 includes twoouter parts 324 and 326 of differing heights. Inside the outer parts324, 326 there is an inclined portion 328 and an inner portion 329. Theinclined portion 328 and the inner portion 329 are configured to conformto the profile of the extrudate support block 290, detailed below inrelation to FIGS. 20a , 20 b.

Referring to FIGS. 20a, 20b , the extrudate support block 290 isgenerally planar and includes a generally flat central surface 330, forsupporting the slider fabric 280. As shown at 332, a rounded edge can beprovided to enable the slider fabric 280 to pass freely through the slot278 onto the flat top or central surface 330.

The support block 290 has side faces adapted to conform to the portions328, 330 of the outlet die blocks 284, 286. Thus, the extrudate supportblock 290 includes, on each side, a first short planar side face 334, aninclined side face portion 336 and in inset planar side face portion338, with the planar side face portions 334, 338 all being parallel toone another.

The side face portions 334, 336, 338 extend upwards to form, on eachside, an upper lip 340. An inner face 342 of each upper lip 340 includesa generally vertical top portion and a rounded lower portion that mergessmoothly into the top surface 330. Viewed in plan, the lips 340 eachhave an inclined section and a straight section, aligned in parallel tothe axis of the die. This configuration is intended to cause edges ofthe slider fabric 280 to fold up progressively around the extrudate.

As best shown in FIG. 20b , the bottom of the extrudate support block290 is provided with a series of narrow ribs 346, so that when mountedon the outlet die blocks, 284, 286 the contact area is minimized, totend to reduce heat transfer by conduction at least between the variouselements of the die. Openings 292 for coolant flow are again shown inFIG. 20 a.

Referring to FIGS. 21a, 21b, 21c , the die blocks 296, 297 and 298, aresimilarly, formed as a similar unit. As best shown in FIG. 21c , slots350 extend partially between the blocks 296, 297. It is here noted thatthe blocks 284, 286 are substantially separated by slots on the sidesand the bottom thereof.

The top surfaces of the blocks 296, 297, 298 are generally planar. Alongthe sides, the forward most blocks 297, 298, show projections 352 and353 of generally similar section, while the rear most block 296 shows aprojection 354 of lesser depth. It will be understood that theprojections 352, 353, 354 are mirror images of each other on eitherside.

The blocks 296, 297, 298 then have central portions, generally indicatedat 358 that project down and provide a generally common outer sidesurface 356 on each side.

The central portion 358 of the rear most block 296 has a profilecorresponding to the rear portion of the extrudate support block 290. Itincludes inclined edges 360. A central surface 362 extends upwardstoward the front of the central portion 358 and inclined side surfaces364 meet the central surface 362 at an angle. Outer side surfaces 366are in a common plane, and incline upwardly at a smaller angle than thecentral surface 362. Outer side edge surfaces 368 are provided. Shallowgrooves 370 are provided to assist in guiding upper edges of the sliderfabric. Within the central surface 362, there is the beginning of arounded surface 370 whose profile is best indicated at 372 in FIG. 21 b.

The rounded surface 370 continues as indicated at 374 into the centralportion of the block 297. This block 297 includes generally verticalshort side surfaces 376, and projecting downwardly and parallel to theside surfaces 374, a narrow projection 378 on each side. The projections378 are intended again to assist in guiding the side edges of the sliderfabric.

The frontmost die block 298 again has a central surface that is roundedand follows the shape shown by the edge 372. The narrow projections 378continue into the die block 298, and terminate before the exit from thedie block 298, so that the extrudate can adopt its final profile beforeexiting from the die.

Referring to FIGS. 22a, 22b, 22c , another cable mandrel 500 has acylindrical plug portion 502 (matching the cylindrical bore 224 shown inFIG. 16a ), and includes a circular flange 504 for bolting the cablemandrel 500 to the first runner plate 220 (FIG. 16a ). Within the plug502, there is an internal bore 506. At the end of the cylindrical plug502, a plurality of small bores 508 are provided in a common plane.Tubes 510 are mounted in smaller diameter sections of the bores 508.Each of the tubes 510 has an inner diameter 514 and a length 516extending between upstream and downstream ends thereof.

The tubes 510 provide a convenient means to convey the cables 50 (alsoshown in FIGS. 3 and 8 e), and may be replaced individually as requiredif damaged or worn. In some particular examples, the tubes 510 may beformed of 304 stainless steel, 16-gage, thin wall, hypodermic tubing(e.g., part number 16T304-36 obtained from Ziggy's Tubes and Wires, Inc.of Pleasant Hill, Tenn.).

The cables 50 are supplied to the tubes 510, and a first polymer issupplied simultaneously to the first runner plate 220 and is deliveredto the combining zone, where it flows around either side of cables 50 toin embed the cables 50 in the thermoplastic flow, thereby forming acomposite extrudate. Along the length 516 of each of the tubes 510, thetemperature decreases towards the upstream end. With this temperaturedifferential, the thermoplastic is sufficiently viscous, intermediate ofthe upstream and downstream ends, to be continuously pushed by thecables 50 out of the downstream end and never reaches the upstream endof the tubes 510.

Although the tubes 510 are shown mounted to the cable mandrel 500, itmay be possible to implement the tubes without having the cable mandrel.For example, tubes can be integrated directly with the runner plate 240(shown in FIG. 16b ). This may avoid problems associated with themandrel, including ensuring an acceptable tolerance between the matingsurfaces of the plug portion 502 and the cylindrical bore 224.

In the extrusion process, high melt pressure (e.g., 1800 to 2800 psi)may be required downstream of the entry of the cables 50 to fullypenetrate the cables 50. As described herein, this penetration ofthermoplastic may increase the life of the cables 50 by separating theindividual strands with a layer of thermoplastic, preferably wearresistant thermoplastic polyurethane, which helps to prevent or at leastreduce the individual strands from galling and abrading while inservice. If the strands make contact in service they may fret, which maycause a gradual loss of tensile strength by abrasion and distortion ofthe cable structure as the steel detritus oxidizes. High penetration ofthermoplastic has been shown to eliminate or at least reduce thisfailure mode with the type of cable that can be used as stretchinhibitor in escalator handrails; for example, high tensile steel cord,brass plated, with a core of three strands of 0.20+/−0.01 mm, and 6outer strands of 0.36+/−0.01 mm.

This high pressure, which may be achieved by the comb unit 400 (shown inFIGS. 18a to 18d ) or other element of restricted flow cross-section,results in a compression of the cables 50 as it enters the melt, at thedownstream end of the tubes 510. Depending on the length 516, looseexterior strands or windings of the cables 50 may progress against theflow of thermoplastic and may eventually get caught at the upstream endof the tubes 510. These loose windings may continue to build up at theentry to the tubes 510 where it can result in cable or even toolingdamage. Based on its appearance, this phenomenon may be referred to“birdcaging” (or otherwise “sleaving”).

One way to control birdcaging would be to minimize the back pressureafter cable entry. However, for reasons described herein, a high meltpressure is desirable, so minimizing back pressure may not be apractical option for handrail extrusion. Another method to controlbirdcaging may be to increase cable tension, but high tension also hasissues in handrail extrusion, as the cross-section is relatively thickand small differences in tension may cause the cables to go off-plane.

It has been determined that if the tubes 510 are of sufficient length,they may prevent or at least reduce the incidence of birdcaging. With asufficient length, each of the tubes 510 may provide enough resistanceto hinder movement so that any loose windings may be continually pushedforward towards the downstream end of the tubes 510 and not reach theupstream end of the tubes 510. The tubes 510 may do this by restrainingthe loose windings to create greater resistance for the slack to pushupstream, rather than downstream with the thermoplastic flow. This hasbeen found to be effective at relatively low cable tension and high diepressure.

Compared to the tubes 310 (shown in FIGS. 17a, 17b, 17d, 17e ), thelength 516 of the tubes 510 has been extended substantially. In someexamples, a length 516 of the tubes may be 200 to 300 times the cablediameter 518. For example, with a cable diameter of 1.1 mm, the length516 of the tubes 510 may be between 220 and 330 mm.

Furthermore, it has been found that larger tube design allows the cablesto open slightly and accept the loose exterior windings. In someexamples, each of the tubes 510 may have an inner diameter 514 that is20 to 30% greater than a cable diameter 518 of the cables 50. This, incombination with a sufficient length 516, may prevent or at least reducethe incidence of birdcaging. In other examples, it may be possible toimplement tubes having non-uniform cross-sections, such that it startslarge (for example, an inner diameter that is 40 to 50% greater than thecable diameter) at the upstream end and tapers progressively towards adownstream end (with, for example, an inner diameter that is 15 to 20%greater than the cable diameter).

While the applicant's teachings are described in conjunction withvarious embodiments, it is not intended that the applicant's teachingsbe limited to such embodiments. The applicant's teachings encompassvarious alternatives, modifications, and equivalents, as will beappreciated by those of skill in the art.

We claim:
 1. An apparatus for extruding an article of uniform cross-section, the article comprising a thermoplastic material and at least one cable for inhibiting stretch of the article, the apparatus comprising: at least one tube for respectively conveying the at least one cable, the at least one tube having upstream and downstream ends, a length extending between the upstream and downstream ends, and an inner dimension; an inlet for the thermoplastic material; and a combining zone in communication with the downstream end of the at least one tube and the inlet, wherein the cable is conveyed through the at least one tube between the upstream and downstream ends, wherein the cable is embedded in the thermoplastic material in the combining zone, wherein the length and the inner dimension of the at least one tube are selected to at least hinder movement of loose windings of the cable from the downstream end towards the upstream end of the at least one tube, wherein the length of the at least one tube is between 200 to 300 times a diameter of the cable, and wherein the inner dimension of the at least one tube is between 20 to 30% greater than the diameter of the cable.
 2. The apparatus of claim 1, wherein the inner dimension of the at least one tube is generally uniform between the upstream and downstream ends.
 3. The apparatus of claim 2, wherein the at least one tube is generally cylindrical so that the inner dimension is an inner diameter of the at least one tube.
 4. The apparatus of claim 1, wherein the at least one tube is mounted to a cable mandrel, and comprising a runner plate secured to the cable mandrel, the runner plate comprising at least one channel for delivering the thermoplastic material to the combining zone.
 5. The apparatus of claim 4, wherein the cable mandrel comprises a cylindrical plug portion, and the runner plate comprises a cylindrical bore for receiving the plug portion.
 6. The apparatus of claim 5, wherein the cable mandrel comprises a circular flange for bolting the cable mandrel to the runner plate.
 7. The apparatus of claim 5, wherein the cable mandrel comprises an internal bore within the plug portion, at an end of the plug portion a plurality of small bores are provided in a common plane, and a plurality of the at least one tube is mounted in the small bores.
 8. The apparatus of claim 4, comprising a comb plate secured to the runner plate, the comb plate comprising slots of reduced flow cross-section to generate back pressure to cause penetration of the thermoplastic material into the at least one cable.
 9. The apparatus of claim 8, wherein the back pressure is between 1800 and 2800 psi.
 10. An apparatus for extruding an article of uniform cross-section, the article comprising a thermoplastic material and a plurality of cables for inhibiting stretch of the article, the apparatus comprising: a plurality of tubes for respectively conveying the cables, the tubes each having upstream and downstream ends, a length extending between the upstream and downstream ends that is between 200 to 300 times a diameter of the cables, and an inner dimension that is between 20 to 30% greater than the diameter of the cables; an inlet for the thermoplastic material; and a combining zone in communication with the downstream end of the tubes and the inlet for embedding the cables in the thermoplastic material.
 11. The apparatus of claim 10, wherein the inner dimension of the tubes is generally uniform between the upstream and downstream ends, and the tubes are generally cylindrical so that the inner dimension is an inner diameter of the tubes.
 12. The apparatus of claim 10, wherein the inner dimension of the tubes is non-uniform between the upstream and downstream ends, and the inner dimension of the tubes is larger at the upstream end than at the downstream end.
 13. The apparatus of claim 10, wherein the tubes are mounted to a cable mandrel, and comprising a runner plate secured to the cable mandrel, the runner plate comprising at least one channel for delivering the thermoplastic material to the combining zone.
 14. The apparatus of claim 13, wherein the cable mandrel comprises a cylindrical plug portion, and the runner plate comprises a cylindrical bore for receiving the plug portion.
 15. The apparatus of claim 14, wherein the cable mandrel comprises a circular flange for bolting the cable mandrel to the runner plate.
 16. The apparatus of claim 14, wherein the cable mandrel comprises an internal bore within the plug portion, at an end of the plug portion a plurality of small bores are provided in a common plane, and the tubes are mounted respectively in the small bores.
 17. The apparatus of claim 13, comprising a comb plate secured to the runner plate, the comb plate comprising slots of reduced flow cross-section to generate back pressure to cause penetration of the thermoplastic material into the cables.
 18. The apparatus of claim 17, wherein the back pressure is between 1800 and 2800 psi.
 19. An apparatus for extruding an article of uniform cross-section, the article comprising a thermoplastic material and a plurality of cables for inhibiting stretch of the article, the apparatus comprising: a cable mandrel comprising a plurality of small bores provided in a common plane; a plurality of tubes for respectively conveying the cables, the tubes mounted respectively in the small bores, the tubes each having upstream and downstream ends, a length extending between the upstream and downstream ends that is between 200 to 300 times a diameter of the cables, and an inner dimension that is between 20 to 30% greater than the diameter of the cables; and a runner plate secured to the cable mandrel, the runner plate comprising at least one channel for delivering the thermoplastic material to a combining zone in communication with the downstream end of the tubes for embedding the cables in the thermoplastic material.
 20. The apparatus of claim 19, comprising a comb plate secured to the runner plate, the comb plate comprising slots of reduced flow cross-section to generate back pressure to cause penetration of the thermoplastic material into the cables. 